Evaluation of catalyst deactivation during catalytic steam reforming of biomass-derived syngas
Bain, R. L., Dayton, D., Carpenter, D. L., Czernik, S. R., Feik, C. J., French, R. J., ... Phillips, S. D. (2005). Evaluation of catalyst deactivation during catalytic steam reforming of biomass-derived syngas. Industrial & Engineering Chemistry Research, 44(21), 7945-7956. DOI: 10.1021/ie050098w
Mitigation of tars produced during biomass gasification continues to be a technical barrier to developing systems. This effort combined the measurement of tar-reforming catalyst deactivation kinetics and the production of syngas in a pilot-scale biomass gasification system at a single steady-state condition with mixed woods, producing a gas with an H2-to-CO ratio of 2 and 13% methane. A slipstream from this process was introduced into a bench-scale 5.25 cm diameter fluidized-bed catalyst reactor charged with an alkali-promoted Ni-based/Al2O3 catalyst. Catalyst conversion tests were performed at a constant space time and five temperatures from 775 to 875 °C. The initial catalyst-reforming activity for all measured components (benzene, toluene, naphthalene, and total tars) except light hydrocarbons was 100%. The residual steady-state conversion of tar ranged from 96.6% at 875 °C to 70.5% at 775 °C. Residual steady-state conversions at 875 °C for benzene and methane were 81% and 32%, respectively. Catalytic deactivation models with residual activity were developed and evaluated based on experimentally measured changes in conversion efficiencies as a function of time on stream for the catalytic reforming of tars, benzene, methane, and ethane. Both first- and second-order models were evaluated for the reforming reaction and for catalyst deactivation. Comparison of experimental and modeling results showed that the reforming reactions were adequately modeled by either first-order or second-order global kinetic expressions. However, second-order kinetics resulted in negative activation energies for deactivation. Activation energies were determined for first-order reforming reactions and catalyst deactivation. For reforming, the representative activation energies were 32 kJ/g·mol for ethane, 19 kJ/g·mol for tars, 45 kJ/g·mol for tars plus benzene, and 8?9 kJ/g·mol for benzene and toluene. For catalyst deactivation, representative activation energies were 146 kJ/g·mol for ethane, 121 kJ/g·mol for tars plus benzene, 74 kJ/g·mol for benzene, and 19 kJ/g·mol for total tars. Methane was also modeled by a second-order reaction, with an activation energy of 18.6 kJ/g·mol and a catalyst deactivation energy of 5.8 kJ/g·mol.